1. Field of the Invention
The present invention relates to electronic imaging systems. More specifically, the present invention relates to techniques and systems for correcting focus aberrations in electronic imaging systems which may be electro-optical.
While the present invention is described herein with reference to a particular embodiment for a particular application, it is understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings of this invention will recognize additional modifications, applications and embodiments within the scope thereof.
2. Description of the Related Art
Focus aberrations in electro-optical systems may be due to variations in the range of objects in a target scene or to fluctuations in the temperature of the sensing elements. Additional aberrations may result from defects in system optics or defects in the processing circuitry. Focus correction may be particularly problematic when the aberration is due to range variations as the effect of focus may not be uniform over a subject frame.
Conventional techniques for correcting focus usually involve open and closed loop electro-mechanical servo control systems which move an optical element, typically a lens, in response to an error signal. Passive and active thermal compensators, for example, move an optical element as a function of temperature. Unfortunately, since these systems are typically open loop, there is often some residual error and there is no provision for range compensation. On the other hand, closed loop autofocus systems minimize focus errors regardless of cause. These systems move an optical element in response to a feedback error signal. Since a single setting is applied to the whole scene, there is no correction for intra-scene range variation effects. Also, a residual diffraction blur typically remains.
Further, these electro-mechanical servo control systems add to the weight, cost and power requirements of electro-optical systems and tend to complicate the design.
There is therefore a need in the art for a system or technique for electronically correcting the focus of electro-optical systems for aberrations due to temperature fluctuations, range variations, diffraction and other effects. Ideally, the system would be noninvasive, allowing for an inexpensive retrofit of existing systems.